Explosive charges used in petroleum boreholes



y 1965 D. CHARRIN 3,196,792

EXPLOSIVE CHARGES USED IN PETROLEUM BOREHOLES Filed Oct. 1, 1962 fl an /J C/7c7/rv/7 INVENTOR.

United States Patent Ofi ice 3,llhd,?@2 Patented July 27, 1965 3,196,792 EIQTLQSEVE CHARGES USED EN PETRQLEUIW BQREHQLFB Denis Qharrin, Paris, France, assignor to Societe de Prospection Electrique Schiumberger, S.A., Paris, France, a corporation of France Filed Oct. 1, 1962, Ser. No. 227,331 Claims priority, application France, Oct. 10, 1961, 875,593 4 Ciairns. (Cl. 1492-44) This invention relates to improvements in explosive charges used in petroleum boreholes and, more particularly, to charges which are directly sunk into the fluid filling said boreholes.

An important problem which arises when using such a type of explosive charge consists in forming the casing and the cap of said charge in a manner such as will satisfy simultaneously the three following imperative conditions:

(1) a suitable confinement at the moment of the explosion with a view to obtaining a maximum efiiciency;

(2) a suitable mechanical behavior and fluid tightness with reference to fluids under high'pressures, to allow the use of the charge at any depth;

(3) the production of small-sized splinters to eliminate any risk of choking the borehole which requires a suitable brittleness of the casing and cap under the action of the shock wave.

it is a well-known fact that it is possible to produce explosive charges satisfying one or two of these three imperative conditions.

Thus, it has been possible to manufacture glass casings and caps in a manner such that the splinters produced upon explosion are of a small size and produce no choking in the borehole. Glass, however, shows poor properties as to confinement which corresponds to a reduction in the available power for a char e of a predetermined size. Furthermore, although glass charges, under good conditions, resist static pressures, considerable care is required in order to prevent any shocks. As to their cost price, it is comparatively high.

it has also been proposed to construct casings of a compact metal, such as aluminum or lead, which satisfy fully the conditions, 1 and 2 above. This type of casing, however, leads to production of very large splinters.

Alternatively, explosive charges of the shaped charge type are sometimes sunk into the boreholes positioned inside fluid tight sleeves, and in such a case, it has already been proposed to make the casing of the charges by means of compressed and sintered metal powder. It is a wellknown fact that sintering consists in keeping the part made of compressed metal powder at a temperature approximating two-thirds of the absolute melting temperature of the metal used, inside a generally reducing atmosphere for a few minutes.

The casings constructed in the above manner show suitable confinement properties at the moment of the explosion and their use inside these fiuid tight sleeves or carriers is entirely satisfactory. Furthermore, under the action of the shock wave produced, the brittleness of casings made of sintered metal is high. For this reason, after the explosion of the charges, those small-sized fragments formed by the casings made of sintered metal are raised with and remain in the carrier. The fragments which have been projected out of the carrier cannot clog the perforations formed in the tubes lining the wall of the boreholes or even the borehole itself, since the broken fragments are sufiiciently small for their local collection not to be objectionable.

Although said shaped charges fitted in fluid tight car riers are suitable for use in boreholes having a substantial or mean diameter, the same does not hold true in the case of boreholes having a small diameter. There, only explosive charges sunk directly into the borehole fluid may be used. For this reason it would be of considerable interest through technical powder metal treatments to construct the casings and the caps of the explosive charges which are sunk directly inside the boreholes, so as to obtain results which are similar to those obtained with the hollow charges carried in fluid tight carriers and equipped with casings and caps made of sintered material. When sunk into the boreholes without any carrier, however, the char es are subjected to the direction action of the fluids under pressure and to unavoidable shocks against the timings. Since the casings of sintered metal have a mechanical resistance which is comparatively small and show a lack of fluid tightness by reason of their porosity, their use for the constitution of charges sunk directly into the boreholes has not been considered hitherto.

On the other hand, rather than use the same type of explosive charge at all depths of firing, it would be advantageous to provide various types of charges, exactly suited for operation under the pressure prevailing at different levels. Of course, these diiterent charges should be fully satisfactory as to the grade of the firing and t0 the broken fragments obtained.

The object of the invention consists in constructing fluid tight explosive charges having casings and caps which associate the properties of confinement and brittleness of sintered parts with the mechanical grade desired.

Various means are already known for the metallurgical treatment of powders with a view to gradually increasing the mechanical behavior of parts made of sintered metal. Thus, through suitable successive thermochemical treatments applied to parts obtained starting from compressed and sintered metal powders, it is possible to bestow mechanical properties which are improved at each treatment, becoming quite comparable to the mechanical properties of parts made of compact metal. It is thus possible to manufacture parts exactly suited for the proposed use thereof for comparatively low cost prices.

Apparatus in accordance with the present invention includes a cake of explosive material and a primer contained inside a casing closed by a cap, the casing and cap being made of a compressed and sintered metal powder of which the main component is iron. This embodiment of the invention is characterized by the fact that the casing and cap have been subjected to at least one thermochemical treatment through the diiiusion of gases. The treatments are defined by the fact that they improve the mechanical properties of the sintered material while they retain also the brittleness with reference to a shock wave, which brittleness is inherent to said sintered material.

in the first embodiment of the invention, an explosive charge is characterized by the fact that the casing and the cap are made of compressed and sintered iron powder which has been subjected depthwise to oxidation in a furnace at 500 C. for about one hour. According to a further feature of the first embodiment, the casing and the cap of such a charge are thenafter impregnated with plastic material.

Through oxidation, a better binding through transformation into intimately welded ferrite granules is obtained for the compressed and sintered iron granules. The impregnation with plastic material closes the pores of the part and makes the charge fluid tight. It is consequently possible to use such an explosive charge inside boreholes at small and mean depths, since in addition to the properties of confinement during the explosion and brittleness under the action of a shock wave which are retained by said treatment, the mechanical resistance of 3 the ferrite obtained has become sufficient for it to support, without any damage, shocks against the wall and pressures rising up to 500 kg. per sq. cm.

In accordance with a second embodiment of the invention, after oxidation of the casing and of the cap originally formed by compressed and sintered iron powder, the casing and cap are placed in a furnace at 1,040 C. for about one hour in an atmosphere of hydrogen. According to a further feature of the second embodiment, the thickness of the cap should be chosen lower than that of the casing. According to another further feature, the casing and the cap are thenafter impregnated with plastic material.

By means of the above treatment, the ferrite granules are reduced and the iron granules produced from large crystals giving the casing and the cap a high mechanical behavior which allows sinking the charges down to depths as which pressures on the order of 700 kg. per sq. cm. prevail. In the shaped charges where the cap is comparatively far from the explosive cake, the cap is given a thickness which is lower than that of the casing. Thus, the brittleness of the cap and casing system is uniform with reference to the shock wave produced by the explosion of the charge, whereas the mechanical resistance of the cap is retained, as similar to that of the casing, since its smaller surface compensates for its reduced thickness.

According to a third embodiment of an explosive charge according to the invention, after oxidation and reduction of the casing and cap originally composed of compressed and sintered pulverulent iron, the casing and cap are placed in a furnace at 900 C. for about one hour in the presence of a gas containing a large proportion of carbon after which they are allowed to cool slowly. According to a first and a second further feature of said third embodiment, the thickness of the cap may be smaller than that of the casing and the casing and the cap may be impregnated with plastic material after the thermochemcial treatments.

A result of this treatment in the presence of carbon is a deep case-hardening of the iron granules. These iron granules are transformed into steel granules so as to give the casing and the cap a mechanical behavior which is hardly inferior to that of parts made of a compact metal and to allow sinking the explosive charges thus obtained into boreholes at considerable depths where pressures of a magnitude of 1,200 kg. per sq. cm. prevail.

Although the mechanical resistance under static pressures is increased, the brittleness of the casing and cap under the action of a shock wave is retained by the cementation. The splinters produced are therefore always small-sized and their local accumulation shows no danger.

According to a fourth embodiment of the invention, the treatments to which the cap is subjected are diiferent from those applied to the casing. Due to this difference the cap, though of the same thickness as the casing and while retaining a mechanical resistance which approximates that of the casing, shows a brittleness with reference to a shock wave which is higher than the brittleness shown by the casing.

Through this arrangement, the respective brittlenesses under the action of the shock wave produced by the explosion of the charge are made similar for the casing surrounding said charge and for the cap which is comparatively far from the latter. The broken fragments produced are small and of a similar size. A further advantage of said arrangement consists in the saving of at least one thermochemical treatment applied for the production of the cap.

According to a still further feature of the invention, an explosive charge having a casing made of compressed and sintered pulverulent iron shows local reductions in thickness in certain areas. This embodiment of the invention is characterized by the fact that after oxidation in a furnace, these areas are impregnated with copper in an atmosphere of hydrogen inside a kiln at 1,040 C. for

about one hour. According to an auxiliary feature, the casing and the cap are impregnated with plastic material.

Through this arrangement there is obtained a uniform mechanical behavior for all the sections of the casing, allowing the use of the charges at greater depths.

The characteristic features and advantages of the invention will appear furthermore from the following description given solely by way of example. Reference is made therein to the accompanying drawing which is an axial cross section of a shaped charge according to the invention.

By way of example also, the following table provides the results of comparative tests conducted on samples of explosive charges in which the casing and the cap of compressed and sintered iron powder have been subjected to identical thermochemical treatments. The tests include, on the one hand, a rise in pressure until a breaking of the walls of the casing of the sample is obtained and, on the other hand, the explosion of typical charges and the checking of the broken fragments. Two thicknesses of caps have been tested: a thickness similar to that of the casing (thick cap) and a thickness smaller than that of the casing (thin cap).

It will be appreciated that for the reasons disclosed hereinabove the use of a thin cap provides, in most cases, homogeneous broken fragments of a small size. It will also be appreciated that the treatment D gives the parts mechanical properties which are slightly superior to those produced with the treatment C. Treatment D is, however, not suitable in the case of explosive charges sunk directly into the boreholes, due to the lack of brittleness under the action of the shock waves of the parts thus treated.

Outer Casing Size of the Broken Thermochemical treatment breaking Fragments pressure, kgJsq. cm.

A. Oxidation in the furnace 500 Thick cap, originally h0- at 500 C. for one hour. mogeneous powder (diam. 0.1 mm.).

B. TreatmeutAplus reduc- 700 Thin cap, homogeneous, 1 tion in a hydrogen atmogn; thick cap, 4 splinters sphiere for one hour at of 20 gr.; remainder, 1 gr. 1,0

C. Treatment B and case- 1,200 Thick cap, 4 splinters of 20 hardening in an atmosgr.; majority of the phere of carbon monoxide broken fragments, 1 gr. to for one hour at 900 C. folpowder; thin cap, homolowed by a slow cooling. geneous, 1 gr.

D. Treatment A followed 1, 500 Thin cap, large pieces of 20 by impregnation with to 30 gr. each, the cap recopper at 26% in a hydromains in one part. gen atmosphere at 1,040 O. for one hour.

The figure shows in true size a casing 1 weighing about 225 gr. Casing 1 is originally made of compressed and sintered pulverulent iron (purity: 98%) which has been subjected to treatment C. The casing is closed by a cap 2 weighing about gr. also composed of compressed and sintered iron powder but which has been subjected to treatment B. The shape of the cap approximates that of a half-sphere and its thickness is similar to that of the casing. To the rear of the casing 1 there is provided a groove 3 occupied during the firing by a detonating blasting cord 4. The area 5 including and surrounding the groove 3 has been subjected to treatment D. Inside the casing are positioned a primer 6, an explosive cake 7 and a conical metal liner 8. A tore-shaped fluid tight packing 9 is provided between the cap and the casing which are secured together by gluing with Araldite at 10. In addition to treatments B, C or D defined hereinabove, the casing and the cap have been impregnated throughout with plastic material. This operation has been performed in two stages: immersion in a bath of liquid plastic material, and then cleaning and polymerization at room temperature.

These methods of production and different treatments aros /o2 55 are used to a great extent for the metallurgical treatment of powders. The cost price of the casings and caps of a shaped charge according to the invention is comparatively low.

A shaped charge thus executed and treated may be sunk directly into a bore hole down to depths at which pressures of a magnitude of 1,000 kg. per sq. cm. prevail since all the sections of the casing and of the cap resist such pressures. The outline and the thickness of the cap 2 enable it as a matter of fact to reliably support said pressures although the casing of a shaped charge which has been subjected uniformly to the treatment B does not support more than a pressure of 700 kg. per sq. cm. At the moment of the explosion of the charge produced through the area 5 by the firing of the blasting cord 4, the following broken material is produced: 270 gr. of parts weighing an average 1 gr. each and 30 gr. of parts weighing an average of 5 gr. each. The injection of plastic material into the pores of the sintered metal, therefore, does not modify the results disclosed in the above table. Consequently, these different splinters do not form a hindrance to the working of the borehole since, in addition to their small size, their speed of settling is similar and well-known (of a magnitude of 130 cm. per second in water).

It is also an easy matter to recover the diiterent splinters when required by means of an electromagnet since they are chiefly composed of iron.

The invention is obviously not limited to the embodiment described and illustrated which has been given solely by way of example in a non-limiting sense. Thus, the treatment applied to the cap may be the treatment C of the above table which would allow a reduction in thickness of the cap While retaining for it a suitable mechanical resistance. Splinters of a still more homogeneous size would apparently be obtained. It is obviously possible to consider for the cap various combinations of treatments and thicknesses.

Furthermore, the treatments provided according to the above table are obviously not the only possible ones. As a matter of fact, a number of the treatments generally resorted to such as nitriding processes may be considered either for the surface improvement of the mechanical properties of compact metal parts, or else for the depthwise modification of the mechanical grade of parts made of sintered iron, provided the brittleness of the parts thus treated is not too much reduced thereby.

It is also possible to replace the treatment D applied to area 5 of the casing by inserting at that point a compact metal part of a suitable shape. Said insertion may be made through soldering, welding, or even through gluin It is thus possible to substantially reduce the thickness separating the blasting cord 4 from the primer 6. It is then possible to use a blasting cord of a lesser power without reducing the performances of the shaped charge.

It is also possible to use cast iron powder instead of iron powder. The treatments to be applied to the parts thus obtained would obviously be thermochemical treatments opposite to those applied to iron parts since, as a matter of fact, it would be necessary in this case to reduce the carbon contents in order to obtain steel or iron whereas, in the preceding case, it was necessary to increase the carbon contents.

Furthermore, the size and the weight of a shaped charge according to the invention obviously may be of any value. The same is the case for the means securing the cap to the casin The arguments given for describing a shaped charge according to the invention will be easily modified for the case where a simple explosive charge is to be considered.

What is claimed is:

1. In a method for producing an explosive shaped charge device for use in a fluid-filled well bore where said device includes a metal case and cover elements constructed from compressed and sintered iron powder and where said elements are normally sealed relative to one another and enclose an explosive with a shaped lined portion for producing a penetrating jet, the improvement comprising the step or" heating at least one or" said elements while in a compressed sintered form to a temperature of 500 C. in an atmosphere of oxygen for about one hour.

2. In a method for producing an explosive shaped charge device for use in a fluid-filled well bore where said device includes a metal case and cover elements constructed from compressed and sintered iron powder and where said elements are normally sealed relative to one another and enclose an explosive with a shaped lined portion for producing a penetrating jet, the improvement comprising the step of heating at least one of said elements while in a compressed and sintered form to a temperature of 500 C. in an atmosphere of oxygen for about one hour, and then heating said one element while said elen ent is in a compres ed and sintered form to a temperature of 900 C. for about one hour in the presence of gas containing a large proportion of carbon.

35. in a method for producing an explosive shaped charge device for use in a fluid-filled well bore where said device includes a metal case and cover elements constructed from compressed and sintercd iron powder and where said elements are normally sealed relative to one another and enclose an explosive with a shaped lined portion for producinga penetrating jet, the improvement comprising thefirst step of heating at least one of said elements while in a compressed and sintered form to a temperature of 500 C. in an atmosphere of oxygen for about one hour, then the second step of heating said one element while said element is in a compressed and sintcred form in an atmosphere of hydrogen to a temperature of 104-0" C. for about one hour.

4-. In a method for producing an explosive shaped charge device for use in a fluid-filled well bore where said device includes a metal case and cover elements constructed from compressed and sintered iron powder and where said elements are normally sealed relative to one another and enclose an explosive with a shaped lined portion for producing a penetrating jet, the improvement comprising the first step of heating at least one of said elements while in a compressed and sintered form to a temperature of 500 C. in an atmosphere of oxygen for about one hour, then the second step of heating said one element while said element is in a compressed and sintered form in an atmosphere of hydrogen to a temperature of 1040 C. for about one hour, then the third step of heating said one element while in a compressed and sintered form to a temperature of 900 C. for about one hour in the presence of gas containing a large proportion of carbon.

References Cited by the Examiner UNITED STATES PATENTS SAMUEL FEINBERG, Primary Examiner. ARTHUR M. HORTON, Examiner. 

1. IN A METHOD FOR PRODUCING AN EXPLOSIVE SHAPED CHARGE DEVICE FOR USE IN A FLUID-FILLED WELL BORE WHERE SAID DEVICE INCLUDES A METAL CASE AND COVER ELEMENTS CONSTRUCTED FROM COMPRESSED AND SINTERED IRON POWDER AND WHERE SAID ELEMENTS ARE NORMALLY SEALED RELATIVE TO ONE ANOTHER AND ENCLOSE AN EXPLOSIVE WITH A SHAPED LINED PORTION FOR PRODUCING A PENETRATING JET, THE IMPROVEMENT COMPRISING THE STEP OF HEATING AT LEAST ONE OF SAID ELEMENTS WHILE IN A COMPRESSED AND SINTERED FORM TO A TEMPERATURE OF 500*C. IN AN ATMOSPHERE OF OXYGEN FOR ABOUT ONE HOUR. 